Almost every modern car has an anti-lock braking system (ABS). But it is not immune to errors. And when something gets wrong with the system, the ABS indicator lights up on the dashboard. What to do in this case? The mechanics from the IAM, Indianapolis used auto dealership explain how to understand what the ABS errors are and how to eliminate it.
The structure and principle of operation of the anti-lock braking system
The first ABS appeared in the 1920s – in the brakes of trains. By the middle of the century, aviation had already picked up the technology. ABS helped airplanes brake effectively and safely during landing. The system settled in the brakes of production cars only in the late 1970s.
The ABS consists of:
- wheel speed sensors;
- ABS control unit;
- valve system and pump combined in the ABS module;
- ABS indicator on the instrument panel;
- connecting cables and tubes.
The system’s operation diagram is quite simple. Each of the sensors installed in the wheel hubs transmits a signal about the rotation speed of its wheel to the control unit. And if, during braking, it loses angular velocity too abruptly and rotates slower than the others, the unit commands to release the pressure in the required circuit of the brake system.
When the brake fluid pressure decreases, the pads are released, and complete blocking of the wheel with subsequent dangerous movement of the car “skidding” is avoided. But as soon as it begins to spin again, ABS increases the pressure in the circuit – thus “balancing” on the verge of blocking.
During sudden braking, the sensors pick up signals about 20 times per second. The vibration on the brake pedal and a characteristic cracking sound indicate the work of the valves of the anti-lock braking system module, which doses the pressure in the circuits.
If at some stage the system fails (damaged contacts, a short circuit in the control electronics, or the control unit receives incorrect signals from the wheel sensors), the ABS error lights up, among other warning lights on the dashboard.
Why did the light come on?
When the ABS icon lights up on the dashboard, you can’t immediately assess the severity of the malfunction. This could be problems with the wheel sensors, faulty wiring, or problems in the ABS control module, which usually combines the electronic controller board, valves, and pump in one housing. A toothed or magnetic ring on the hub by which the sensors determine the speed of rotation of the wheel can become clogged with dirt or dust from the brake pads.
In practice, the ABS control module rarely fails even on older cars. However, a blown fuse can easily be the reason why the ABS indicator on the dashboard lights up.
Most often, problems with the ABS occur in the most vulnerable places to external influences – under the bottom. The ABS error lights up due to dirt and sensor failures, broken wiring, corrosion of contacts, and the like. The result is the same: the ABS lamp on the dashboard lights up, and the system turns off.
Troubleshooting
It is recommended to search for the problem with the least labor-intensive procedures. And before doing anything, you should make sure there is a problem. To do this, you can accelerate to 25 mph on a straight road and brake sharply. Make sure there are no other road users. Then, based on the marks on the asphalt, it is easy to understand whether the wheels were locked. It also happens that the warning light is on, but the system is working. Moreover, sometimes the indicator goes out after such braking – and the ABS returns to the operating mode.
If braking does not help, the wheels are locked, and the ABS is still on the panel, the second logical step is to check the fuse. This is the simplest thing you can do yourself. It is enough to lift the cover of the fuse box under the hood. The required fuse is marked with the ABS symbol.
Even without special knowledge, you can check the contacts of the system control unit. It is worth doing this if, for example, the ABS sign on the dashboard lights up and then goes out. We look under the hood for a metal “box” to which 4 or 5 brake system tube fittings are connected, as well as the only large plug – the power connector.
Before disconnecting the plug from the ABS unit, disconnect the negative battery terminal. Then, you can safely check the integrity of the contacts (sometimes they rot) and make sure there is no short circuit, oxidation, or moisture. It is still better to entrust the replacement of the connector in the event of its complete failure to specialists.
If the ABS light is still on, you should get to the hubs and wheel sensors using the jack. The primary task is to check the integrity of their wiring. Due to the oxidized contact, the control unit “loses” the sensor and displays an ABS error on the dashboard.
Wiring rubbed against suspension parts, or the body can dangle freely, touching the metal. Over time, the insulation of the wires can rot or dry out with the same result – a short circuit to the car body. This is also worth keeping in mind if the ABS lights up.
But if everything is in order with the wiring and the ABS light does not go out, you should remove the sensors one by one. The goal is to clean the sensor seat on the hub and its contact area with the crown from dirt and moisture.
Both the sensor itself and its contact group may require replacement. However, according to statistics, the main reason for the ABS “control” light on the dashboard is still stuck shavings – wear of the pads and discs.
However, by having a scanner at hand or contacting a service center, you can much faster find an ABS malfunction – the car’s control unit itself will indicate which of the wheels is the problem.